'unornamental' originates from English, specifically formed from the negative prefix 'un-' (from Old English 'un-') meaning 'not' and the adjective 'ornamental', which ultimately comes from Latin 'ornamentum' (from 'ornare') where 'ornare' meant 'to adorn or furnish.'

'ornamental' changed from Latin 'ornamentum' into Old French 'ornement' and Middle English 'ornament', eventually becoming the modern English adjective 'ornamental'. The form 'unornamental' is a Modern English negation formed by adding the prefix 'un-' to 'ornamental'.

Initially, Latin 'ornamentum' referred to a 'decoration or accessory'; over time 'ornamental' came to mean 'decorative', and 'unornamental' developed to mean 'not decorative' or 'plain'.